Abstract: Based on the background of agricultural conditions, especially the soil water characters in semi arid area of Loess Plateau, and on combining with the progress in field of root to shoot communication, the research and developmental potential of root chemical signals were discussed in this paper. The core of water saving agriculture in this area is to increase crop's water use efficiency (WUE). The ways for increasing WUE should be included: 1)decreasing inefficient evaporation from soil surface, and 2)increasing roots in deep soil, decreasing those in top soil, optimizing resource allocation pattern, and increasing reproductive allocation proportion. Root chemical signals affect strongly all the two aspects. According to the present accumulation of knowledge, the study on effects of root chemical signal on crop productivity can reveal some important theoretical problems.

Key words: Loess Plateau, Semi arid area, Water use efficiency, Root to shoot communication, Root chemical signal, soil inorganic carbon, carbon stable isotope, soil organic carbon, δ¹³C value, Junggar Basin